A Different Theory Makes A Different Observer

Pike (1982: 3):

The list and kind of things men will find will vary radically if they adopt different theories as tools with which to search for these units. The theory is part of the observer; a different theory makes a different observer; a different observer sees different things, or sees the same things as structured differently; and the structure of the observer must, in some sense or to some degree, be part of the data of an adequate theory of language.